Intaglio printing is a process by which a printed image is formed upon paper or other printing substrate material by passing the material, frequently in web form, between a pair of press rolls. In the process, the rolls are thrust together under high pressure to compress the substrate therebetween to transfer ink from an inked image on an engraved or etched plate cylinder or sleeve carried by one of the rolls to the substrate surface. High pressure processes of this type include rotogravure printing processes in which a high resolution plate is made to carry an inked image in recesses engraved into the plate surface from which the ink to be pressed from the grooves when the plate is brought into high pressure contact with the paper. The use of the extreme pressure facilitates the transfer of ultra high resolution line images to the paper. Such processes are useful in printing money and other certificates where the printing must be of extremely high quality.
Intaglio presses employ a pair of rollers or printing cylinders, including a plate cylinder which carries the image to be transformed to a paper substrate, and an impression cylinder which underlies substrate and forms a supporting surface against which the plate cylinder presses the paper during printing. In the printing process, high pressure is exerted upon the paper by the pair of cylinders compressing it from opposite sides.
In fine quality, high resolution intaglio printing processes such as those employed for the printing of currency, bank notes and the like, these pressures may be exceptionally high, even up to 10,000 pounds per linear inch across the width of the print rolls. The maintenance of a uniform high pressure across the width of the rolls is important to the production of high resolution, high quality printed images. This requires that the roller supporting structure be such that the contact between the impression and plate cylinders be maintained uniformly across the width of the rollers as they contact the substrate.
The response of the prior art to the need to provide high uniform pressure across the width of print rolls has been to apply, and control the application of, force at least at both ends of the printing cylinders or press rolls, and often to exert force on the rollers at multiple points across the width of the printing surface. The direction of the prior art has been to subject the rollers to a distributed or multipoint force, acting upon the rollers, which produces a certain amount of undesirable roll deformation, and to further distribute or modify the force to correct for the deformation of the rolls. Such deformation, if produced and uncorrected, results in the unwanted non-uniformity of printing pressure across the width of the rolls. The structures employed to correct the deformation have been complex and less then totally effective.
Another problem with prior art intaglio presses has been the time required to service the printing rolls. These rolls must be removed for periodic maintenance and to permit replacement of the impression sleeve carried by the impression cylinder. The sleeves are subject to heavy wear and in some installations must be replaced as often as every two days. Prior art roll constructions have required an excessive amount of time to change rolls. For example, in a typical press, a half a day is required.
For small article low pressure printing and embossing processes, printing presses have been provided with a printing roller rotatably mounted to a shaft which are supported to a frame at one end. Such presses for example are shown in Hale U.S. Pat. No. 573,407, Sherwood U.S. Pat. No. 720,629, Barton et al U.S. Pat. No. 1,599,868, Price, Jr. et al U.S. Pat. No. 3,405,633, Heuss U.S. Pat. No. 4,188,874, and German U.S. Pat. No. 687,191. Such methods of supporting rollers in a printing press upon a cantilevered shaft provides for easier means interchanging of the plate cylinders than where rollers are mounted to shafts supported at both ends. However, the mounting of cylinders in cantilevered fashion has never been successful to support rolls for high pressure engagement as is required for intaglio printing.
One proposed intaglio press construction using cantilevered rolls is disclosed in Heuss U.S. Pat. No. 4,188,874. In the press disclosed in that patent, one or both of the press rolls are cantilevered. However, no means is provided for applying forces to the roller shafts to shift the shafts relative to one another to create a high printing pressure. Rather, a special roll referred to as a pressure equalization roll is employed as one of the rollers. The pressure equalization roller uses internal hydraulically actuated supporting elements in order to distribute the pressure across the width of the roller to compensate for roller distortion. This construction is not a practical approach to providing a high pressure intaglio press with a uniform pressure across the rollers.
Prior art press construction has also employed a variety of roll mounting devices used in such a way as to affect the roll positions. Several printing presses, for example, have employed pressure roller sleeves supported by a multiplicity of bearings disposed adjacent to the longitudinal axis of the roller to support the cylinders on the shafts. Such presses are shown in Hornbostel U.S. Pat. No. 3,161,125, McDermott U.S. Pat. No. 3,561,658, Pflaum U.S. Pat. No. 4,372,205, Maier U.S. Pat. No. 4,438,695, George et al U.S. Pat. No. 4,487,122, and German Offenlegungsschrift No. 2,849,202. In the presses described in such patents, however, any uniformity of pressure between the mating rollers is achieved by using roller supporting shafts mounted at both ends to a frame.
Notwithstanding the state of the printing art, the high pressure presses which have been developed to date have failed to provide for rapid and easy interchange of printing rolls and plates. The problems of providing uniform high pressure contact between the plate and the paper have resulted in conditions which have aggravated the problem of roll interchangeability. Accordingly, there exists a need for providing a cylinder support for intaglio presses which will provide a uniform high pressure across the rolls and which will provide rapid removal and replacement of the rolls.